Thermodynamic and electrophysical investigation of new nanostructured lanthanum and sodium copper–zinc manganite $\rm LaNa_2\rm CuZnMnO_6$

We study the temperature dependences of the specific heat of nanostructured lanthanum and sodium copper–zinc manganite $\rm LaNa_2\rm CuZnMnO_6$ by dynamic calorimetry in the temperature range $298.15$–$673$ K. The curve of specific heat dependence on temperature at $348$ K shows a jump, probably related to a phase transition of the second kind. We derive the equations for the temperature dependence of the specific heat, taking the phase transition temperature into account. The standard entropy is calculated, and the temperature dependences of the thermodynamic functions of the studied manganite are determined. The temperature dependence of the electrical resistance is studied in the range of $293$ to $483$ K using an LCR meter (Taiwan); at $343$ K, the possible semiconductor conductivity transforms into a metallic one; and at $443$ K, the metallic conductivity transforms into a semiconductor one. The bandgaps are calculated.